Fish & Bacteria Need Oxygen in Pond Water

Page Summary: To say that oxygen is important is a gross understatement. Almost everything on earth depends upon that mixture of Oxygen, Nitrogen, Carbon Dioxide and other trace gases we call air to survive. A pond is no different... fish, amphibians, algae, and most forms of aquatic life with the exception of anaerobic bacteria (ie bacteria that do not need oxygen to survive and multiply) also need oxygen to go about their daily lives. In a fish pond the koi or goldfish extract oxygen that is dissolved in the water. As this oxygen is depleted then more oxygen enters the pond water body at the air water interface. The bigger the interface (eg turbulent water such as waves or air bubbling through the body of pond water) the more oxygen will be transferred to the pond water. Cold water can hold more oxygen than warm water. This is why trout live in colder climates or higher altitudes in warm countries. Koi and goldfish are vert tolerant of wide ranges of oxygen concentration in water.

One of the most important ingredients in the quest for a flourishing, healthy garden fishpond is oxygen. If you want to add new life to your koi pond, increasing the level of dissolved oxygen is certainly a promising route to success.

What Does an Air Pump do?

Air pumps work by condensing atmospheric air and conveying it under pressure to an aeration device, most often a diffuser. The air pump that employs a rubber diaphragm is most commonly used by koi keepers. The pump is made up of an electronmagnet and a permanent magnet that work by moving the rubber diaphragm rapidly back and forth. In this way, air is suctioned into the diaphragm, compressed and expelled through one-way valves.

Air pumps are rated according to power consumption, flow rate and the pressure at which air can be delivered. The deeper your pond, the deeper the air has to be delivered. This should be the criteria that you use to weigh up whether a particular pump is powerful enough to convey air to the bottom depths of your koi and goldfish pond.

Types of Aeration

A flowing water feature – moving or flowing water is the only natural means to oxygenate a pond. In natural bodies of water, energised streams and rivers contain a higher oxygen content than placid lakes and ponds. It’s quite obvious then how the addition of a waterfall to your koi pond can be of benefit. However, it may not be the solution to the oxygen requirements of a fully-stocked koi and goldfish pond, as the water that pours into the pond from the waterfall won’t really reach the bottom layers of the pond.
Venturi - one of the less efficient pond aeration devices, a venturi is a cylindrical hollow mechanism that water is pumped through. It looks somewhat like an hourglass, and its unique shape causes atmospheric air to be sucked in with the water. Oxygen is thus instilled into the water that is being pumped back into the garden koi pond. As impressive as a venturi looks, it is not very efficient as it involves the pumping of water as opposed to just air. The bubble size produced is relatively large, which also reduces the rate of oxygen diffusion and ensures that only the top layers of pond water receive the full benefit oxygen exchange.
Diffusers – these are definitely the most effective pond aeration devices and there a variety on offer to koi and gold fish keepers, from disposable airstones to efficient airdomes. Diffusers work by producing an ongoing supply of fine bubbles that rise through the water in a column. Fine bubbles are much more effective for increasing dissolved oxygen levels than larger bubbles as the surface area for oxygen transfer is significantly increased. Contact time between the rising air bubbles and the pond water also plays a crucial role in oxygen exchange. Finer bubbles create a drag against the water due to their increased surface area and this allows for longer contact time which inevitably allows time for increased oxygen exchange. In terms of choosing a method of diffusion, the comparatively newer airdomes have more advantages than the customary airstones. Airdomes are installed onto a bottom drain and aerate from the lower water levels. Whereas airstones produce larger bubbles if the air supply volume is increased and often become blocked, airdomes provide enhanced aeration and are self-cleaning - making them the better choice for koi pond aeration.

You'll be amazed at how simple it can be to breed fish with the help of spawning brushes. You'll need one mature female and at least two males.

Put the brushes one above the other at the edge of the pond. Spawning usually occurs in the early morning after a night of flurried activity and can take several hours. Most of the eggs will stick to the brushes which can then be taken out of the pond and put in filtered water of the same temperature. If the eggs are not separated from the adult fish they may be eaten.